Check the data sheets for the capacitors. If they are a good brand and series they should last much longer than IBM's
But still, since they are cans of corrosive material, they may leak or dry out. 20, 30, maybe 40 years, but still.
If you can't find suitable poly caps or ceramics, I'd say use a tantalum, but only get it from trusted manufacturers, and get a higher voltage rating than the originals. The last thing you'd want is a tiny fire in your M2.